1. Field of the Invention
This invention relates to a method and apparatus for cleaning materials moving in an endless path by application and/or extraction of fluid.
2. Description of the Prior Art
It is known to use conveyor belt-like materials in the manufacture of certain products; as, for example, paper and paper-like products. In the papermaking process such belts are porous in nature and are commonly referred to as papermakers' fabrics, felts or wires. As a result of their continuous use during the papermaking process there is a tendency for the porosity of such belts to vary as their surface and/or internal portions (interstices) begin to accumulate (a) quantities of the furnish or pulp-like material used in the manufacture of paper, and (b) other contaminants found in the papermaking environment. Such variation in porosity is undersirable in that it adversely affects the quality of the paper being produced. For example, the non-uniformity of the porosity of a papermakers' felt which travels in an endless path in the press section of a papermaking machine will cause non-uniform dewatering of the paper web being carried through the press section by such a felt. It is known that such non-uniform dewatering may adversely affect the surface characteristics of the finished paper product. Passage of a belt such as a press felt through a press section nip formed by a pair of press rolls also tends to continuously compress the felt which eventually causes permanent deformation of the fibrous materials which comprise the felt. Such elimination of the bulky nature of a press felt may affect its operational characteristics at least to the extent that its ability to carry water and to contact the pulp material without marking the paper web may be adversely affected.
In order to clean, rebulk or otherwise recondition such porous belts, various apparatus have been developed. For example, in the papermaking process it is known to utilize an oscillating high-pressure needle shower which generally functions as a result of the recirprocatory motion of a plurality of nozzles, each of which directs a jet of water against the surface of a moving papermakers' felt. Such reciprocatory motion is generally in a direction transverse to the direction in which the endless felt travels. In operation, the cleaning cycle of such nozzles is determined by trial and error taking into consideration variables such as the type and length of the felt, nozzle reciprocation speed and spacing, and the paper machine speed. In using such devices, uniform and total felt coverage is premised upon a uniform oscillating motion of the shower nozzles and a paper machine operating at a constant speed. However, in such structures, even a momentary change in the speed of the paper machine or the oscillating shower nozzles will tend to eliminate the synchronization of the nozzle speed vis-a-vis the felt speed which will, in turn, cause non-uniform and less than total cleaning and reconditioning of the felt. To overcome this problem apparatus has been described in Shelor, U.S. Pat. No. 3,910,815, which attempts to synchronize the speed of a papermakers' felt with the speed of a nozzle means as it travels from one edge of the felt to the other. Such synchronization is generally accomplished by providing a traversing vehicle which includes nozzle means and which travels across the width of the felt at some predetermined speed that is directly related to the felt speed. For example, in the preferred embodiment described in the Shelor patent the traversing vehicle is ultimately driven a predetermined distance by a stepping motor which causes such movement in response to a power pulse received from a pulse generator coupled to one of the press rolls. In operation, the pulse generator emits a specified number of electrical pulses for each revolution of the coupled press roll to actuate the stepping motor and cause the traversing vehicle to move a predetermined distance. In this manner synchronization of felt speed with the speed of the nozzle means is controlled by the speed of the press rolls; that is, as the revolutions per minute of the press rolls increase the revolutions per minute of the papermakers' felt increase, and as the revolutions per minute of the press rolls decrease the revolutions per minute of the papermakers' felt decrease. However, when the papermakers' felt stretches during operation it would be necessary for the machine operator to first observe such stretch and then to properly adjust the speed of the press rolls or nozzle in order for synchronization to be maintained. If the machine operator did not observe that the press felt had stretched, then synchronization would be eliminated until such time as an adjustment was made in the speed of the press rolls or nozzle to compensate for such stretch. Until such an adjustment was made, the cleaning pattern which the oscillating shower traverses would become non-uniform to the extent that (a) some areas of the felt might not be subjected to the nozzle emission, and (b) those areas of the felt which were subjected to the nozzle emission might not be subjected to the same degree of exposure. These problems are especially significant when such shower units are used with press felts since it is known that a press felt is particularly subjected to various increases in length throughout its life. Accordingly, in order to maintain the desired synchronization of the felt speed vis-a-vis the speed of the nozzle using a device of the type described in the Shelor patent, it would be necessary to continuously monitor the felt length on the paper machine. Additional monitoring would be required throughout the life of the felt to assure that machine speed would be adjusted to compensate for any further increases in length of the felt due to stretch. We do not believe that such monitoring and adjustments by the machine operator are practical or desirable in the ordinary papermaking environment.
Shower units of the type described in the Shelor patent appear to be designed to utilize nozzle means affixed to a single traversing vehicle. By so limiting the number of nozzles there may be a tendency for a reduction in the uniformity of the cross machine or transverse direction porosity. This occurs as a result of the fact that, by the time such vehicle traverses across the felt, areas of the felt first subjected to the emission of the nozzles have again become plugged or otherwise contaminated with the area of the felt furthest removed from the shower unit, measured in the cross-machine direction, being most affected; the area of the felt towards its middle portion being less affected; and the area of the felt in the vicinity of the shower unit being the least affected.
It is an object of the present invention to provide an apparatus for cleaning endless belts which is simple in construction.
It is another object of the present invention to provide an apparatus for cleaning endless belts having a minimum number of mechanical parts.
It is a further object of the present invention to provide an apparatus for cleaning an endless belt which subjects all areas of the belt to the same degree of exposure to a cleaning fluid.
Still a further object of the present invention is to provide an apparatus for cleaning an endless felt which uniformly rebulks, reconditions and cleans all areas of such felt.
Yet a further object of the present invention is to provide a shower element which moves in the transverse direction such that it is continuously and automatically synchronized to the speed of an endless belt.
Another object of the present invention is to provide a shower element which moves in the transverse direction such that it is continuously and automatically synchronized to the revolutions of a papermakers' fabric or felt to provide uniform cleaning of the fabric or felt regardless of whether the length of the fabric or felt or the speed of the machine changes.